Freshwater reserves found under the sea

Scientists have discovered huge reserves of fresh water several kilometres out to sea from Australia, China, North America and South Africa. Writing in the journal Nature, they state that there are “large volumes of low-salinity groundwater that are found below continental shelves” - around 0.5 million km³ worth, in fact.

Lead author Dr Vincent Post, of the National Centre for Groundwater Research and Training (NCGRT) and the School of the Environment at Flinders University, said this volume of water is “a hundred times greater than the amount we’ve extracted from the Earth’s sub-surface in the past century since 1900” and could “sustain some regions for decades”.

Dr Post said groundwater scientists knew of fresh water under the sea floor, but thought it only occurred under rare and special conditions. “Our research shows that fresh and brackish aquifers below the seabed are actually quite a common phenomenon,” he said.

He explained that the reserves were formed over the past hundreds of thousands of years, when the sea level was on average much lower than it is today and the coastline was further out. “So when it rained, the water would infiltrate into the ground and fill up the water table in areas that are nowadays under the sea.

“When the sea level rose when ice caps started melting some 20,000 years ago, these areas were covered by the ocean. Many aquifers were - and are still - protected from sea water by layers of clay and sediment that sit on top of them.” 

The aquifers are similar to the ones below land, which much of the world relies on for drinking water, and Dr Post said their salinity is low enough for them to be turned into potable water - certainly much lower than that of seawater, meaning the desalination process would be less energy-intensive.

“Freshwater on our planet is increasingly under stress and strain, so the discovery of significant new stores off the coast is very exciting,” said Dr Post. “It means that more options can be considered to help reduce the impact of droughts and continental water shortages.” Furthermore, he said, these options can be assessed against each other in terms of cost, sustainability and environmental impact.

But Dr Post warned that those nations closest to the water reserves should take care in how they manage this non-renewable resource, which “won’t be replenished until the sea level drops again”.

“Sometimes boreholes are drilled into the aquifers for oil and gas exploration or production, or aquifers are targeted for carbon dioxide disposal. These activities can threaten the quality of the water,” he said.

The study authors further noted that the discovery of the water reserves has the potential to “contribute to the advancement of other scientific disciplines, in particular sedimentology and marine geochemistry”.

Source